Control of nosocomial infection and exposure to infectious disease is of paramount concern to doctors, nurses, and clinicians who work in hospitals and surgery centers. One of the most effective methods for controlling infection is regimented hand disinfection before and possibly after each patient contact and particularly before and after each surgical procedure. Hand disinfection is generally accomplished using antimicrobial soaps with water. These soaps are usually formulated to include either povidone-iodine (usually 7.5% by weight) or chlorhexidine digluconate (CHG) (usually 2% or 4% by weight) as the active antimicrobial agent. In addition, these formulated soaps may contain surfactants and possibly low levels of humectants such as glycerin.
Hand disinfection is also accomplished using presurgical scrub replacements. These are used instead of the soap and water scrub. Presurgical scrub replacements ideally achieve bacterial kill equal to or better than a traditional soap and water scrub and in a shorter period of time. Additionally, they maintain or improve the skin's natural barrier to microbial and chemical contamination while providing acceptable tactile properties. Examples of presurgical scrub replacements include hydroalcoholic gels which generally include high levels of either ethanol or isopropanol as the disinfecting agent and also include a thickener and optionally a humectant (e.g., glycerin). To date, thickeners used in hydroalcoholic gels have been based on anionic polymers such as polyacrylic acid (sold under the tradename "CARBOPOL" by BF Goodrich Specialty Polymers and Chemicals Division of Cleveland, Ohio). U.S. Pat. No. 4,915,934 (Tomlinson) discloses the use of CHG-containing antiseptic foams based on hydroalcoholic solvents, a fatty alcohol, and a surfactant. The surfactant is selected from the group of ethoxylated sorbitan alkylates, ethoxylated fatty alcohols, and ethoxylated nonyl phenols.
Formulating stable viscous hydroalcoholic emulsions is difficult for two reasons. First, addition of short chain alcohols (such as ethanol) to an aqueous system decreases the surface tension dramatically. For example, 40% by weight ethanol in water has a surface tension of approximately 31 dynes/cm compared to pure water which has a surface tension of about 72 dynes/cm at 20.degree. C. A hydroalcoholic solution at 60% by weight ethanol has a dramatically decreased surface tension as compared to water. Such a composition has a surface tension of approximately 27 dynes/cm at 20.degree. C. Second, many surfactants typically used in cosmetic emulsions become completely or partially soluble in hydroalcoholic systems.
In bulletin 51-0001-259 regarding skin care, Specialty Chemicals of ICI America of Wilmington, Del. state that although ethanol can provide several benefits to skin care emulsions, formulators often avoid ethanol because it is difficult to prepare stable emulsions in its presence. In fact, the bulletin also states that ethanol is often used to break emulsions.
U.S. Pat. No. 4,956,170 (Lee) discloses a hydroalcoholic skin moisturizing/conditioning antimicrobial gel. The gel comprises 60-75% by weight ethanol and 0.4-2% by weight of an anionic carbomer polymeric thickening agent. The formulations also comprise polyethoxylated nonionic surfactants/emulsifiers to stabilize the added emollient oils in addition to a fatty alcohol. U.S. Pat. No. 5,167,950 (Lins) discloses an antimicrobial aerosol mousse having a high alcohol content. The mousse comprises alcohol, water, a polymeric gelling agent and a surfactant system comprising a C16-C22 alcohol, aerosol propellant, and a nonionic polyethoxylated surfactant. These systems are based on neutralized polymeric acrylic acids, which are anionic and therefore incompatible with positively charged molecules such as chlorhexidine digluconate. Furthermore, these systems, while cosmetically acceptable, do not shear thin readily and can feel heavy with a somewhat tacky feel under gloves.
Novel Gelling Agents Based on Polymer/Surfactant Systems, E. D. Goodard et. al., J. Soc. Cosmet. Chem., 42, 19-34 (Jan/Feb. 1991) discloses polymer/surfactant thickener systems for completely aqueous systems based on quaternary polymers in combination with anionic surfactants. These thickener systems, however, are not effective in hydroalcoholic solvent systems.
In other hydroalcoholic systems, such as those described in U.S. patent application Ser. Nos. 08/493,714 and 08/493,695 (both of which were filed on Jun. 22, 1995 and assigned to 3M Company), nonionic, anionic, cationic, or zwitterionic emulsifiers are used as thickeners, without the need for a polymeric thickener such as polyacrylic acid. Although these systems are highly desirable, other high viscosity hydroalcoholic compositions useful as an antimicrobial lotion, for example, are still needed.